As far as I can tell, the physical OIS is on by default in both auto and manual modes.
There's also a further 'steady OIS' that only becomes available to select If you don't have UHD selected.
If I have UHD selected OIS is greyed out - I would think that would mean OIS is disabled but something is keeping it steady as this is apparent in both stills and videos, in auto and video mode. I can only assume that OIS is always enabled but that the OIS setting refers only to digital video stabilisation, which is only available in HD and FHD. Confusing huh?